In recent years, laser technology has been remarkably advanced. In particular, downsizing and output power up have been made in solid lasers, semiconductor lasers and gas lasers emitting lights in the ultraviolet, visual and infrared ranges of 300 nm to 1200 nm in wavelength. Accordingly, these lasers are highly useful as exposure light sources in direct plate making from digital data available from computers and so on. Studies have been intensively made on recording materials sensitive to these various laser beams. Namely, a positive recording material suitable for infrared lasers which is sensitive to wavelength of 760 nm or longer (see, for example, U.S. Pat. No. 4,708,925) and an acid catalyst-crosslinked negative recording material (see, for example, JP-A-8-276558) are known. Moreover, radical polymerization negative recording materials suitable for ultraviolet lasers or visual lasers are also known (see, for example, U.S. Pat. No. 2,850,445 and JP-B-44-20189).
In general, the recording system employed in such a negative image recording material is as follows. Namely, the material contains a compound emitting radicals by the action of light or heat and a polymerizable compound. Using the radicals emitted by light or heat as an initiator, a polymerization reaction is induced and thus the recording layer in the exposed part is hardened, thereby forming an image part. These negative image recording materials suffer from a problem of being inferior in image forming properties to positive image recording materials in which a recording layer is solubilized by laser irradiation energy.
To elevate the sensitivity, therefore, attempts have been made to employ high-power infrared lasers. In such a case, however, there arises another problem that the recording layer undergoes ablation during laser scanning and thus contaminates the optical system. Furthermore, attempts have been made to employ a chemical amplification recording material (see, for example, JP-A-11-65105) and a recording material with the use of polymerization of a compound having an ethylenic unsaturated bond (see, for example, JP-A-2000-89455). However, these recording materials contains component highly reactive with light or heat. Therefore, undesired reactions frequently occur when handled under a white light lamp or due to a change in the environmental temperature during storage. That is to say, it is feared that these materials are poor in storage stability.
Although a recording material containing a vinyl resin having (meth)acrylate group in its side chain is known as a recording material using polymerization of a polymer compound having an ethylenic unsaturated bond in its side chain (see, for example, JP-A-2002-62648), such a material has only poor printing tolerance. Although a recording material containing a polyurethane resin having (meth)acrylate group in its side chain is also known (see, for example, JP-A-2002-251008), such a material suffers from problems such as having poor development properties in a nonimage part. These problems are seemingly caused by the fact that, since the unsaturated bond is introduced in a large amount into the side chain of the polymer compound for improving sensitivity, interactions between side chain substituents worsens the development properties or interaction between main chains, which closely relates to image strength, is inhibited by steric factor of the side chain substituents, thereby lowering the printing tolerance.
Accordingly, it has been required to develop a lithographic printing plate precursor having well-balanced sensitivity, storage stability, printing tolerance and development properties.